The present invention relates to a process for the hydrogenation of D-glucuronic acid to yield L-gulonic acid.
L-gulonic acid, the preparation of which is an object of the present invention, is valuable as an intermediate in the preparation of xylitol. In a representative procedure, L-gulonic acid may be oxidatively decarboxylated by a Ruff degradation of yield L-xylose as described in references including E. Fisher, O. Ruff, Ber. 33 2142 (1900). The L-xylose obtained may be reduced to xylitol by methods described or referred to in U.S. Pat. No. 4,075,406 or described, with reference to the reduction of glucose to sorbitol, by L. W. Wright in Chemtech, January, 1974, p.42.
The reduction of D-glucuronic acid to yield L-gulonic acid with sodium amalgam in a weakly alkaline solution was reported by Thierfelder in Z. Physiol. Chem., 15, 71 (1891). A similar reduction of sodium D-glucuronate monohydrate utilizing sodium borohydride as the reagent is described by M. L. Wolfrom and K. Anno in J. Am. Chem. Soc., 74, 5583 (1952). In a somewhat different procedure, a sodium borohydride reduction of D-glucuronolatcone resulted in preferential reduction of the carboxyl, rather than the aldehydic, group, see D. L. MacDonald and H. O. L. Fischer, J. Am. Chem. Soc. 78, 5025 (1956).
Catalytic hydrogenation of D-glucuronic acid using a nickel catalyst was reported in Example 4 of German Patentschrift No. 618,907 issued Sept. 5, 1935. However, as demonstrated in the Comparative Examples which follow, use of nickel will require a relatively high temperature which causes degradation of the starting material. Nickel catalysts often require reprocessing after use since they may be deactivated during or after the reaction. Therefore, nickel has disadvantages as a catalyst in continuous processing.
A further teaching in the art of the reduction of D-glucuronolactone with a nickel catalyst to yield L-gulonolactone is found in the article "A New Action of Anion Exchange Resins on the Lactone Ring of Some Carbohydrates" by Ishidate, et al appearing in Chem. Pharm. Bull. 13(2) pages 173-176 (1965). However the starting material was only used in a concentration of about 10% by weight of the solution at room temperature. Further, the workup of the product was complicated in that after filtration of the catalyst, the filtrate was concentrated to a syrup and crystals were formed by the addition of dry ethanol.
It is an object of the invention to provide a relatively low temperature reaction route from D-glucuronic acid to L-gulonic acid whereby a product is obtained which freely crystalizes from solution after partial evaporation in high yield and with a minimum of by-products which would complicate recycling of unreacted starting material. It is also an object of this invention to provide a continuous catalytic process for the preparation of L-gulonic acid from D-glucuronic acid whereby the catalytic hydrogenation catalyst may be utilized for long periods of time without catalyst reactivation. It is also an object of the invention to provide an economical process for the preparation of L-gulonic acid in terms of energy input, durability of catalyst cost of separating product and of discarding by-products.
A further object of the invention is a process for the production of L-gulonic acid from a concentrated solution of the starting material, thus resulting in a more economical use of facilities.